The present invention relates to a tracking control system for grooveless disc records, and in particular to such systems wherein the tracking error caused by the tilting of the disc record is eliminated.
Tracking control systems for grooveless records involve the use of an optical sensing device which emits a laser beam onto the record and a pair of adjoining optoelectrical elements on which the reflecting beam is made to be incident. The laser beam incident on the record surface is modulated in intensity in accordance with the surface variation of the record which is in the form of a series of microscopic pits having a depth approximately a quarter wavelength of the laser. The reflected light, thus varying between high and low discrete values corresponding respectively to the pits and the land portions of the record, is directed to the optoelectrical elements to form a beam spot thereon so that when the optical axis of the sensing laser is out of the path of a track, the beam spot on the optoelectrical sensing elements is displaced from a neutral line which exists between them. The output signals of the optoelectrical elements are fed to a differential amplifier or subtractor to detect the difference between them to provide a tracking control signal which is used to control the lateral position of the laser beam. However, the disc record has a tendency to tilt with respect to the horizontal. When this occurs the beam spot on the optoelectrical sensors will deviate erroneously producing a false tracking control signal.